Update using-azure-identity.md (#18887)

Recently, we moved the authorization-code-credential sample into the manual tests folder, since this sample is really intended to test the credential and not to showcase a real world scenario (I plan on making improved samples with this credential in the upcoming months).

I didn’t notice that those changes were breaking a link we had at this level. Thanks to Daniel Jurek for letting me know about this issue.

documentation/using-azure-identity.md

@@ -309,7 +309,7 @@ locally, you can also add a redirect URI for your development endpoint
 (e.g. `http://localhost:8080/authresponse`).
 
 A complete example of hosting your own authentication response endpoint can be
-found in the [`authorization code sample`](https://github.com/Azure/azure-sdk-for-js/blob/main/sdk/identity/identity/samples/manual/authorizationCodeSample.ts).
+found in the [`authorization code manual test`](https://github.com/Azure/azure-sdk-for-js/tree/main/sdk/identity/identity/test/manual/authorization-code-credential).
 
 ### DefaultAzureCredential